A Savannah River National Laboratory researcher has been restricted from doing radiological work for the rest of the year after purportedly receiving a dose of radiation that pushed the person past an acceptable annual threshold, according to a statement from the lab.

Savannah River Nuclear Solutions, the management and operations contractor at the Savannah River Site, is "confident" the worker was not exposed while at work, according to the statement, which was provided by a spokesperson. The contractor, which oversees the lab, investigated the matter. That process included examinations of the researcher's job location and coworkers.

A July 18 weekly report from the Defense Nuclear Facilities Safety Board, an independent watchdog group, stated the dose was "much greater" than what the worker would likely be exposed to both at work and off the job. The radiation dose was also inconsistent with a list of potential exposure scenarios, the report notes.

The report does not speculate beyond that.

The issue was noticed during a quarterly review of the researcher's thermoluminescent dosimeter, a small device that can be worn on a lanyard to monitor personal exposure to radiation.

The employee's monitoring device had not malfunctioned, according to the safety board dispatch.

The annual level that was breached was "significantly lower" than the U.S. Department of Energy federal limit, according to the lab statement.

People are exposed to radiation on a daily basis, though the levels are relatively low. A cross-country flight and medical X-rays are some common sources. Most so-called "background" exposures come from radon in the air, according to the U.S. Nuclear Regulatory Commission.

Colin Demarest covers the Savannah River Site, the U.S. Department of Energy, the National Nuclear Security Administration and government in general. Follow him on Twitter: @demarest_colin